Power Supply Circuit for PMDC Motor Controller-28V-4A

This circuit is the part of a bigger project – 3 Speed PMDC Motor Controller without using a micro-processor.

PMDC means Permanent Magnet DC Motor. PMDC Motors can deliver high starting and acceleration torque and predictable motor speed. It’s compact in size and highly energy efficient. The application ranges from battery powered wheel chair, power tools, conveyors, door controllers, welding & X-Ray equipment, tomography systems, pumping equipments and numerous other applications.

Most of the PMDC Motors are rated at 12V or 24V, and some Motors are rated at 36V DC. The Power supply circuit is an integrated unit to supply 12V-28V (adjustable) for Motor supply, 12V DC for control circuit and +5V DC for Logic Circuits.

electronics15.com_circuit_28V-4A_dc power suplly

 A 30V / 5A transformer delivers 30V AC to a 10A Bridge Rectifier block. The output of the bridge rectifier will be about 34/35V DC and is smoothened by a 3300MFD / 50V electrolytic capacitor to get pure DC Voltage at the Input of the LM1 – 317T Regulator.

LM1 is a TO-225 package variable voltage regulator whose output can be adjusted to get 12V to 28V DC (as may be required) by P1 (5K Trimpot). The output of LM1 passes through a TO-3 Transistor 2N3055 to boost the current to 5Amps. The output is available at the emitter of T1 which is the input of LM2 – LM317T. LM2 is a TO-3 package regulator and supplies 12V DC for the control relay circuit. The output of LM2 is the input of LM-3 which is a  TO-3 Package 7805 regulator. The LM-3 output is +5V DC for the control logic circuit.

Regulator Package details and pin connections are provided in the circuit diagram.

Here is the Bill of materials (BOM) for the above circuit:


The above circuit is designed and tested by Sonu Perito. If this circuit is useful to you, please provide a feedback.

career help

Scope of an electronic engineer in large industries and corporate sectors.

 What jobs can you do with an electronic engineering degree?

Let’s take a tour to the relevant industries where electronic engineer has good prospects. The obvious choice may be the companies which produces electronics product. In my opinion, this may not be the only choice. Your selection should be guided by pay package, job stability, and reputation of the company and scope of learning.

Welcome to electronics15.com_your Career help

                                            Fig-1- Scope of electronic engineer in industries

Look at the image above (Fig-1), and you will find that the options are much broader both within the engineering industries and outside the electronics industries.

It’s obvious that each industry will have will have typical requirements for electronics engineers. This blog will focus on these typical requirements and prepare you to face the challenges during interview and also during your professional career. Let’s find out this typical job requirements for different industries.

1. Electronics Sector:

Here an electronics engineer has two major roles:

(a) Design Engineer: To design a Product or prototype of a Product or designing a component prior to launch. Product design requires in-depth knowledge & experience in electronics and this may not be suitable for a fresh graduate engineer.

(b) Application Engineer:  any fresh graduate engineer can become an application engineer (supporting a product for its entire life) after successful completion of installation & commissioning training on the products.

2. Automotive Industry:

Electronics is an significant division in Automobiles. Today, engine control systems, dashboard indicators, sensors, air-conditioning, safety systems and info-attainment systems in automobiles are designed by electronics engineer. This website will deal with electronics in automobile engineering in great details.

3. Defense Sector:

Electronics plays a vital role in manufacturing and application of Defense Products. Here an electronics engineer has to operate in cross-discipline like a mixture of mechanical, electronics and electrical engineering knowledge. Sensors, actuators and automation are some of the important areas in defense sectors. Electronics15.com will cover all the above to a large extent.

4. Power Generation Engineering:

The job openings are mainly as maintenance engineer. Here electronics engineer has to maintain Instrumentation & control systems in plant and adequate knowledge of SCADA, DCS, Instrumentation engineering, Telephony and Data Networks are necessary. This website will cover all the requirements in power generation sector.

5. Railways Engineering Sector:

Electronics engineers are involved in Signaling systems, Advanced Rail movement & controls, Safety Control equipment and advanced Telecom and Networks. The Magelv Bullet Train has opened up a new job prospect for electronic engineers. The train uses state-of-the-art  technology to propel by magnetic force and hover above the track at very high speed.

6. Elevator & Escalator:

The elevator world is changing rapidly. Our sweet mother earth has limited space at ground level and that too cannot be increased. The only way is to go up and up and build skyscrapers to accommodate a living space / office space for everyone.

A tower like Burj Khalifa in Dubai is 828 meter high. Engineers have to build a high speed elevator which travels at a speed of 36km/hr or 10m/sec to match the tower height. This elevator is a Double Decker elevator and fastest in its class. The elevator built for the skyscraper Taipei101 is faster and travels at a speed of 60km/hr or 16.83m/sec.

These high speed and ultra-high speed elevators are built with advanced technology to take care of the elevator speed, passenger comfort at such a high speed and above all the safety of the passenger.

Electronics engineers have tremendous scope in elevator and escalator engineering. We’ll extensively cover this subject.

7. Food and Beverages sector:

Automation and Robotic Integrations are finding extensive applications in Food & Beverages sector. Electronics engineers are playing very important roles in these sectors. This website will completely cover this sector.

Fig-2 below is an example of fully automatic plant controls in a modern biscuit factory.

welcome to electronics15.com_modern automatic biscuit plant

                                          Fig-2 – Automatic Biscuit Manufacturing Plant

  1. Petro-chemicals, Oil & Gas Sector:

Electronics engineers having a sound knowledge of Instrumentation engineering, Sensor Engineering and Automation technology will be hired by this sector at a comfortably high salary level.

9. Aerospace Industry:

The insertion of power electronics in aerospace technologies is becoming widespread. The application of semiconductor devices and electronic converters are used in the International Space Station, satellite power system, and motor drives. Advanced electronics technology is applied to aircraft, starter/generators and reusable launch vehicles. Flywheels, servo systems embodying electro-mechanical actuation, and spacecraft on-board electric propulsion are being used. Electronics engineers have enormous scope here.

10. Pharmaceutical, Cosmetics and Medical Industry:

These industries have to avoid bare hand contact and so Automation and Robotics are an integral part in manufacturing processes in these industries. Electronics engineers have tremendous scopes in designing and implementation of automatic process control equipment.

11. Ship Building Industries:

Modern ships have sophisticated on-board automatic electronics equipment and automatic ship controls including navigational gadgets. Ship building companies are hiring electronics engineers to bring up to date controls and automation in ships.

Electronics Engineers has scopes in the following industries: Construction, Solar & Wind Energy, Transport, Energy, Machine Building and Building Automation.

We have listed scopes of an electronics engineer in large industries and corporate sectors. Should you require any help during job search or job interview, please click “contact us” and send your requirement, we will help you as much as possible.

Automatic Voice Announcer

Automatic Voice Announcer

The global spread of science and technology and the growing commercial access to advanced technologies with possible applications in all fields are creating equipment and gadgets helpful to humans to make life easier and safer. To assist in performing this task, electronics15.com engineers are designing electronic products which are both commercially and socially important. One such product is automatic voice announcer.

We are more comfortable in listening than reading or writing. The effectiveness and popularity of voice announcers in elevators / lifts, precautionary announcements to prevent dangerous practices in industries, helpful location announcements in large scale trade fairs, trains and airports and other innovative announcements are giving birth to advanced Automatic Voice Announcers.

What is an Automatic Voice Announcing System?

Voice Announcer is an audible indicator. The audible signal is pre-recorded which plays automatically when the respective channel is triggered. The triggering actions are pre-programmed and controlled through a micro-processor. The triggering can be done through sensors, digitally controlled touch panels, mobile phones or signals through computer controlled interfaces. The strength of audible signal depends on the particular applications and has to be 10 dBA to 80 dBA depending on the particular application.

What is dBA?

A-weighted decibel, abbreviated dBA, or dBa, or dB(a), are an expression of the relative loudness of sounds in air perceived by the human ear. In the   A-weighted system, the decibel values of sounds at low frequencies are reduced compared with weighted decibels, in which no correction is made for audio frequency.

Fig-1 below is a standard Voice Announcer Card:


Fig -1

The announcement words will depend on the particular use of the Voice Announcer. Like an elevator voice announcer will announce the name or the number of the current floor with a human voice for the passengers inside the car or cabin. It also announces safety matters and evacuation techniques in case of emergency. It also plays sweet background music while the lift is travelling.

Here is an example of elevator voice pre-recorded messages:

  1. Attention please! You have reached Ground Floor.
  2. Do not be alarmed. This car is needed for a medical emergency. When the door opens, please exit in a safe and orderly manner.
  3. Do not be alarmed. This car is transferring to emergency power. When the door opens, please exit in a safe and orderly manner.
  4. Do not be alarmed. This car is now in fire fighters return service. When the door opens, please exit in a safe and orderly manner.
  5. Please exit the car.
  6. This car is full.
  7. Please allow the door to close (nudging)
  8. This lift is g When the door opens, please exit in a safe and orderly manner.
  9. This lift is going down.
  10. This lift is going up.

Elevator Voice Announcer keeps riders moving in right direction and cautions the riders with emergency messages and evacuation directions during fire, earthquakes or any other natural disasters.

Technicalities of a Voice Announcer:

We will refer to Fig-2 – Voice Announcer Block Diagram:

Atypical Block Diagram of Voice Announcing System

Atypical Block Diagram of Voice Announcing System

A standard voice announcer card (refer to fig-1 & 2) is composed of Opto-coupler, a micro-processor controlled voice processor, programmable flash or OTP (one time programmable) memory chip, and an audio amplifier with loud speaker.

Signals either in digital form or switching signals are generated at the application centers like Elevators, Home Automation Equipment, Bus & Bus Terminus Announcement equipment, Airports & Airlines Announcing Equipment, Bullet Train Announcing equipment and many other application centers. These signals are isolated through Opto-coupler before it is received by the micro-controller based voice processor. The voice processor receives pre-recorded signals either from Flash programmable chip or from OTP – one time programmable chip in analog signal form.

These analog signals are amplified by an Analog Amplifier and played back through the Loudspeaker for pre-planned announcements.

Sonu Perito is an expert in Voice Announcer Systems. He is a professional designer of Voice Announcers for different application.

Anyone interested to know more about Voice Announcers or wants to manufacture Voice Announcers, please click “contact us”.